Modern aircraft include many components that generate heat, including, but not limited to avionic electronics, radar, next generation directed-energy systems. Adequate thermal management of these components is critical to the successful operation of aircraft. When components generate a large amount of heat, the heat must be transported quickly away from the heat source in order to prevent failure of the heat producing components.
In the past, thermal management of avionic components have included air-cooling systems and liquid-cooling systems. Regardless of the type of fluid used (e.g., air or liquid), it may be challenging to deliver the fluid to the heat source, e.g., the component generating large amounts of heat. For example, avionics modules may include processors and/or integrated circuits within enclosures that make it difficult for a cooling fluid to reach the heat generating component.
To transfer the heat away from these difficult to access components, plates made from highly conductive material, such as graphite or metal, have been placed in thermal contact with the heat generating components such that the heat is carried away via conduction through the plate. However, the speed and efficiency of the heat transport in a solid plate is limited by the thermal resistance of the material.
As illustrated in FIG. 1, the prior art has also employed heat pipes to transfer heat from a heated region 102 (also referred to as an evaporator region) to a cooled region 104 (also referred to as a condenser region). A traditional heat pipe 100 consists of a tube 101 with a wick 110 running along the interior surface of the tube 101. The tube 101 is filled with a liquid that evaporates into a vapor at the evaporator region 102, which then flows toward the condenser region 104 (the vapor flow is shown as 140 in FIG. 1). An internal volume of the tube 101 where the vapor may flow may be referred to as a vapor region 120. The vapor condenses back into a liquid at the condenser region 104. The wick 110 enables the condensed liquid to flow back to the evaporator region 102 for the cycle to repeat (the liquid flow is shown as 130 in FIG. 1).
While heat pipes are able to transfer a large amount of heat, a major barrier to using heat pipes in airborne environments is the tendency for heat pipes to experience “dry-out,” whereby the liquid in the evaporator region 102 is fully vaporized and the wick becomes void of liquid. When dry-out occurs, the temperature of the evaporator region may rise sharply, causing catastrophic damage to the heat generating components being cooled by the heat pipe. Various aspects of the heat pipe may cause dry-out by not allowing the liquid to travel to the evaporator region 102, including wick resistance, bubble formation within the wick, and prevention of adequate wicking due to gravitation and acceleration forces.
Removing the wick from the heat pipe eliminates some of the barriers associated with using heat pipes in avionics. It is known to use non-wicking forces to transport liquid back to the evaporator region of a heat pipe. One such technique is a oscillating heat pipe, examples of which are shown in FIG. 2. Heat pipe 200 represents an open-ended oscillating heat pipe and heat pipe 210 represents a closed oscillating heat pipe. A oscillating heat pipe includes a chamber holding a liquid, with a portion of the chamber in thermal contact with a heat source and another portion in thermal contact with a condenser. The liquid near the evaporator boils and evaporates, producing a vapor bubble in the chamber. As the vapor bubble expands, the pressure within the bubble increases such that it pushes the liquid, creating a nascent flow of the liquid. When the bubble reaches the condenser region, the vapor bubble (also referred to as a “slug”) condenses and the pressure drops. A reverse liquid flow commences whereby liquid flows to the evaporator region. The process repeats and an oscillatory fluid motion is achieved.